Table of Contents
Introduction:
Aortic dissection (AD), a critical condition with an incidence of 35 cases per 100,000 individuals aged 65 to 75 years annually, often involves Stanford type B dissection, constituting 25 to 40 percent of cases. While thoracic endovascular aortic repair (TEVAR) has transformed type B aortic dissection treatment, challenges arise with a minimum of 15 mm of normal aortic wall required for effective stent graft fixation, impacting the patients due to an inadequate proximal seal zone. To extend the sealing zone, intentional coverage of the left subclavian artery is performed, but it raises risks like stroke and spinal cord ischemia.
Despite Society for Vascular Surgery guidelines recommending LSA reconstruction, the optimal technique remains unspecified, with options including chimney graft, single-branched stent graft, physician-made fenestration, and carotid-subclavian bypass. Additionally, the shift to TEVAR has reduced morbidity and mortality rates.
What Is the Subclavian Artery?
Subclavian Artery: Situated just below the clavicles, the subclavian arteries supply blood to the upper extremities, head, and neck. The right subclavian artery stems from the brachicephalic trunk, while the left originates directly from the aortic arch.
Running laterally between the anterior and middle scalene muscles, the subclavian arteries extend to the lateral border of the first rib, transforming into the axillary artery. The branches include the internal thoracic artery, vertebral artery, dorsal scapular artery, thyrocervical trunk, and costocervical trunk. Embryonically, the left subclavian arises from the seventh intersegmental artery, while the right subclavian develops proximally from the fourth aortic arch, medially from the dorsal aorta, and distally from the seventh intersegmental artery.
Adjacent to the subclavian arteries, various components of the nervous system, such as the sympathetic trunk, parts of the brachial plexus, vagus nerve, phrenic nerve, and right recurrent laryngeal nerve, coexist. Venous pathways like the internal jugular and vertebral veins closely link with these arteries, forming an interconnected system supporting cellular processes in the neck, upper extremities, thyroid gland, and brain.
Clinically, the subclavian artery may exhibit congenital or idiopathic pathologies, addressable through physical rehabilitation or surgery. An aberrant subclavian artery, a common congenital anomaly, is typically benign but may be symptomatic in 20 percent of cases. Thoracic outlet syndrome, affecting the middle or distal ends of the arteries, can result in flow obstruction, leading to neurological and ischemic changes in the upper extremities. Conditions like Takayasu arteritis may cause inflammatory changes in the subclavian arteries, presenting with bilateral bruits and ischemic effects. Subclavian steal syndrome, involving primary artery stenosis leading to retrograde flow, can ‘steal’ blood from the circle of Willis, impacting brain blood supply. Rare issues include subclavian arterial aneurysms or congenital stenosis due to anatomical variations.
What Is Thoracic Endovascular Aortic Repair?
Thoracic endovascular aortic repair (TEVAR), approved by the U.S. FDA, has emerged as a minimally invasive alternative for thoracic aortic pathologies like aneurysms and dissections, offering favorable perioperative outcomes compared to open surgery. Despite its advantages, TEVAR does not significantly reduce the risk of postoperative stroke when compared to open surgery.
An essential consideration in TEVAR is enduring sufficient proximal sealing of the graft to exclude aortic pathology effectively. Approximately 40 percent of TEVAR patients have lesions extending to or involving the left subclavian artery origin, necessitating LSA coverage. This coverage poses risks such as reduced blood flow to the left vertebral artery, potentially leading to cerebrovascular ischemia and stroke. The Society of Vascular Surgery guidelines recommend routine LSA revascularization in TEVAR procedures covering the LSA to mitigate stroke risk.
The advent of TEVAR brought about reduced operative time and length of stay, and improved morbidity and mortality rates, particularly as it expanded to treat various pathologies. However, TEVAR has limitations, notably the need for disease-free seal zones in the proximal and distal aorta. In cases where the proximal seal zone, especially beyond the LSA, is inadequate, coverage of the LSA is necessary. Still, it raises the risk of stroke, spinal cord ischemia, and upper extremity ischemia.
Indications:
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Aortic aneurysms.
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Traumatic aortic transection.
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Management of type B dissection.
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Penetrating aortic ulcer or intramural hematoma.
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Thoracoabdominal aneurysms.
What Is Subclavian Artery Revascularization and Its Procedure?
The subclavian artery revascularization procedures include carotid-subclavian bypass (CSB) and subclavian transposition:
CSB is the most commonly performed LSA revascularization procedure due to its familiar exposure and technical simplicity. The surgery involves a transverse incision above the clavicle, extending from the medial head of the sternocleidomastoid to the midclavicle. Dissection starts laterally, progressing through the scalene fat pad to identify the subclavian artery. A short prosthetic conduit is typically used for the bypass, with the subclavian anastomosis performed first. The bypass is then tunneled onto the common carotid artery in the retrojugular plane. The subclavian artery dissection avoids the main thoracic duct but requires meticulous control of smaller branches to prevent lymphatic leakage.
Subclavian-to-carotid transposition is a less common revascularization method, avoiding prosthetic conduit use and negating the need for separate embolization or proximal subclavian artery management. Contraindications are rare but include an early origin of the vertebral artery and a patent left internal mammary to coronary artery bypass graft.
The incision is made between the two heads of the sternocleidomastoid muscle, creating subplatysmal flaps and dividing the omohyoid muscle. The vertebral artery is transposed separately, if needed, with careful attention to the ligation of the thoracic duct. This technique allows for tension-free anastomosis to the carotid artery and a short arterial stump at the level of planned thoracic endovascular aortic repair (TEVAR) coverage.
For both CSB and subclavian transposition, meticulous hemostasis is crucial, and leaving a drain is not routinely necessary as long as there is no lymphatic leak and proper hemostasis is ensured at the end of the procedure, including protamine reversal if needed.
Thoracic Branched Endoprosthesis: This commercially available device addresses thoracic aorta pathologies, particularly those involving the LSA, in patients at high risk for debranching subclavian procedures. It is suitable for cases with morbid obesity, potential for duct or nerve injury, and carotid stenosis. Specific anatomical landmarks determine the clinical feasibility of the device. Access considerations involve iliofemoral access for the larger device, with radial or brachial access for through-and-through access. Successful deployment requires precise wire separation, and alignment of the portal with the subclavian may necessitate graft rotation. Lowering systolic blood pressure during deployment is preferred.
Chimney and Periscope Techniques During TEVAR: Primarily used in emergencies or cases with challenging arch branch vessels, these techniques involve subclavian chimney or periscope stenting. Access points include left upper extremity and bilateral femoral access. A covered stent is placed outside the thoracic endovascular aortic repair graft, and simultaneous TEVAR and chimney stent deployment reduces gutter leak risks. These techniques are considered bailout maneuvers in complex endovascular repair.
Laser Fenestration Furing TEVAR: Reserved for emergency scenarios and high-risk patients ineligible for open surgery or traditional interventions, laser fenestration involves left arm brachial access, bilateral femoral access, and a steerable sheath. The TEVAR graft is deployed, and a laser fiber perforates the fabric, creating a fenestration.
Balloon dilation and covered stent placement follow, with careful verification of intraluminal passage. Proximal branches can undergo similar fenestration, offering a tailored approach for specific cases, such as aortic pseudoaneurysms requiring intricate TEVAR into zone 1 with additional branches.
Conclusion:
Subclavian artery revascularization is critical to managing various thoracic and aortic pathologies. Traditional surgical methods like carotid-subclavian bypass and transposition remain reliable, providing excellent long-term outcomes. However, the evolving landscape introduces minimally invasive alternatives and endovascular techniques, such as thoracic branched endoprosthesis, chimney, periscope, and laser fenestration during TEVAR. These advancements offer tailored solutions for complex cases and high-risk patients.
